In a differential amplifier, which statement best describes its primary function?

In a differential amplifier, which statement best describes its primary function?

• A. Recording the differences in the voltages of two inputs
• B. Recording the differences in the voltages of the active input and ground
• C. Recording the differences in the voltages of an exploring electrode and the patient ground connection
• D. Recording only identical voltages received by its two inputs

Answer: (A)

A differential amplifier is designed to capture and amplify the difference between two input voltages while rejecting signals that are common to both inputs. In a sleep study, that means it subtracts one electrode’s voltage from the other, producing an output proportional to their difference. This is why the best description is that it records the differences in voltages of two inputs—the two electrodes. This approach matters because it minimizes noise that is shared by both leads, such as mains interference or widespread bodily noise, thanks to high common-mode rejection. The device is not measuring one input against ground; that would be a single-ended measurement and would be more susceptible to that shared noise. If both inputs happened to be driven to the same voltage, the differential output would be zero (in an ideal amplifier), so it isn’t about recording identical voltages.

A differential amplifier is designed to capture and amplify the difference between two input voltages while rejecting signals that are common to both inputs. In a sleep study, that means it subtracts one electrode’s voltage from the other, producing an output proportional to their difference. This is why the best description is that it records the differences in voltages of two inputs—the two electrodes.

This approach matters because it minimizes noise that is shared by both leads, such as mains interference or widespread bodily noise, thanks to high common-mode rejection. The device is not measuring one input against ground; that would be a single-ended measurement and would be more susceptible to that shared noise. If both inputs happened to be driven to the same voltage, the differential output would be zero (in an ideal amplifier), so it isn’t about recording identical voltages.